1. Field of Invention
The present invention relates to an apparatus for producing finger jointed lumber and, more particularly, to an apparatus for applying longitudinal compression to pairs of interlockable rigid wood elements aligned end to end to form a completed finger joint therebetween.
2. Description of the Prior Art
Apparatus for applying end pressure to pairs of boards having finger jointed, or aligned serrated ends, is in more or less common use for the production of finger jointed lumber. Generally, the surfaces of the finger joints are coated with glue or other adhesive and then mated together by hand. The finger jointed boards are then conveyed through apparatus which apply longitudinally compressive forces to the boards, sufficient to facilitate complete interengagement in the joint.
Heretofore finger jointing apparatus has generally comprised coacting pairs of drive and holdback units positioned for the engagement of preassembled finger jointed lumber by each. Such units have utilized torque driven rollers formed of solid resilient material and arranged in pairs to provide the drive and holdback functions. A differential in the speed of rotation between first and second pairs of rollers produced longitudinal compression in the lumber conveyed therebetween as the first set of drive rollers conveys the lumber at a speed greater than the second set of drive rollers will allow.
Drive and holdback units have also included combinations of rollers and pressure plates. In such arrangements, the rollers are mounted in the apparatus ingress portion to serially feed successive boards under a retractably mounted rigid bearing plate functioning much like a brake shoe to exert a retarding force to the boards. Such apparatus, though effective in assembling finger jointed boards, is limited in operation. Solid rollers have a single resiliency factor and often tend to crush small boards. Rigid drag plates cannot automatically adjust for variations in material thickness or material curvature. When drive and holdback rollers are used in combination the distance between the tangential engagement points may be determinitive of the minimum board length conveyed therethrough, generally longer than 8 inches. In such apparatus, variations in the shape of successively fed boards of minimum length often result in misalignment and joint failures. Thus, the lumber length, uniformity and shape become limitations in the operation of the above apparatus.
It is inherent in the woodworking industry to create boards of lengths less than 8 inches during cutting and trimming operations, as well as boards which vary in shape and thickness. Such lumber could otherwise form feed stock for conventional finger jointing mechanisms were the apparatus available which could handle their size and dimensional variations. With the growing shortage of lumber in the world, the need has been fostered for making use of such scrap material. This need, as well as the requirements of conservation and economy, has necessitated the creation of new and improved apparatus to form finger jointed lumber.